Previous studies established that GTP-binding regulatory proteins (G- proteins) can be extracted from hepatic and brain membranes with octyglucoside as large structures (>12S) suggestive of multimers. Exposure of these membranes to activating guanine nucleotide (GTPgammaS) alone or with hormone (glucagon, with liver) caused the large structures to break down into structures similar is size to heterotrimeric G-proteins. Several types of G-proteins were shown to have different size multimers depending on the type of detergent used for extraction; each G-protein type displayed distinct sensitivity to the "depolymerizing" actions of GTPgammaS. Synaptoneurosome membranes treated with p-phenylenedimaleimide were shown to contain cross-linked G-proteins that, on sizing columns, resemble the polymeric forms of actin and tubulin in these membranes. These findings coupled with the detergent studies and target size analysis of adenylyl cyclase systems suggest that membrane receptors are linked to multimeric structures of G-proteins. A new concept of hormone action is proposed which takes into account the multimeric structures of G-proteins and which suggests that the coupling and dynamics of receptor/G-protein interactions are controlled by the binding and hydrolysis of GTP, analogous to the ATPase-controlled interactions of multimeric actin and myosin.